Near field performance of staged diffusers in shallow water
Name
MIT-EL-79-015-06454612.pdf
Size
6.13 MB
Format
Adobe PDF
Checksum (MD5)
108b6aae5af063934555c6b92874c315
Author(s)
Adams, E. Eric
Trowbridge, John Howard
Date Issued
April 1979
Publisher
MIT Energy Laboratory
Series/Report no.
MIT-EL
79-015
Abstract
Submerged diffusers are commonly used to dilute condenser cooling
water from coastal power plants. A staged diffuser, in which the
diffuser centerline is perpendicular to shore and the nozzles are direc-
ted essentially offshore, is often used at sites where there is a long-
shore, reversing current. Because of the symmetry of this design,
dilution is improved by a longshore current in either direction, and
the diffuser's position perpendicular to shore allows it to intercept
a crossflow effectively.
The performance of a staged diffuser in shallow water of constant
depth has been analysed previously by treating the diffuser as a
continuously distributed line source of momentum (Almquist and Stolzen-
bach, 1976). This theory has been reviewed and extended to consider
the case of a sloping bottom and to compute the external (entrainment)
flow field set up by the diffuser. In these analyses the important
parameters are the gross diffuser dimensions, including total flow
rate, discharge velocity, water depth and diffuser length. Length
scales are on the order of one diffuser length, and the characteristics
of the individual jets are assumed to be insignificant in describing
diffuser performance at this level.
A more detailed analysis of staged diffuser performance in the
near field is useful if one wishes to describe the temperatures and
shear stresses experienced by organisms that are entrained into the
diffuser plume. Length scales in this problem are on the order of the
port spacing, and characteristics of the individual jets are very
important at this level. Relevant diffuser dimensions are discharge
velocity, port diameter D , port spacing, port elevation h, water
depth H, and discharge orientation.
A description of the near field at this level has been obtained
by solving for the trajectories, velocities, temperatures and flow rates
of individual jets. Boundary layer approximations are made similar to
those used in the classical analysis of free turbulent jets, and the
analysis includes the effects of shallow water, the flowfield set up
by adjacent jets, and an ambient current. Theoretical predictions
are compared with the results of an experimental program. The analysis
is then used to evaluate different diffuser designs from the stand-
point of temperature and shear stress exposure of entrained organisms.
Description
This work was performed by John H. Trowbridge as part of his masters thesis in the M.I.T. Dept. of Civil Engineering, 1979.
Subjects
Diffusers
Pipe |x Hydrodynamics.
Waste heat.
Thermal pollution of rivers, lakes, etc.
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